Before the 1500's, the western plains of North America were dominated by farmers. One group, the Mandans, lived in the upper Missouri River country, primarily in present-day North Dakota. They had large villages of houses built close together. The tight arrangement enabled the Mandans to protect themselves more easily from the attacks of others who might seek to obtain some of the food these highly capable farmers stored from one year to the next.

The women had primary responsibility for the fields. They had to exercise considerable skill to produce the desired results, for their northern location meant fleeting growing seasons, winter often lingered; autumn could be ushered in by severe frost. For good measure , during the spring and summer, drought, heat, hail, grasshoppers, and other frustrations might await the wary grower.

Under such conditions, Mandan women had to grow maize capable of weathering adversity. They began as early as it appeared feasible to do so in the spring, clearing the land, using fire to clear stubble from the fields and then planting. Form this point until the first green corn could be harvested, the crop required labor and vigilance.

Harvesting proceeded in two stages. In August the Mandans picked a smaller amount of the crop before it had matured fully, this green corn was boiled, dried, and shelled, with some of the maize slated for immediate consumption and the rest stored in animal-skin bags. Later in the fall, the people picked the rest of the corn. They saved the best of the harvest for seeds or for trade, with the remainder eaten right away or stored for later use in underground reserves. With appropriate banking of the extra food, the Mandans protected themselves against the disaster of crop failure and accompanying hunger.

The women planted another staple, squash, about the first of June, and harvested it near the time of the green corn harvest. After they picked it, they sliced it, dried it, and strung the slices before they stored them. Once again, they saved the seed from the best of the year's crop. The Mandans also grew sunflowers and tobacco; the latter was the particular task of the old men.

重点单词：
western : n. 西方人,西部片,西部小说;a. 西方的,西洋的,西部的
plain : n. 平原,草原;a. 简单的,明白的,平常的,清晰的,普通的,朴素的;ad. 清楚地;n. 无格式
dominate : vt. vi. 支配,占优势
upper : a. 上面的,较高的,上级的,上院的,穿在外面的,地表的,北部的,后期的;n. 鞋帮,绑腿,上齿
Missouri : n. 密苏里州
primarily : ad. 主要地,首先地,基本地
tight : a. 紧的,吝啬的,严厉的;ad. 紧紧地
enable : vt. 使能够,使能
protect : vt. 防卫,保护,警戒
attack : n. 攻击,抨击;vt. 攻击,抨击,动手;vi. 攻击
seek : vt. 寻求,寻找,探索,请求,追求,搜索;vi. 寻找,搜索
obtain : vt. 获得,达到;vi. 流行
capable : a. 有能力的,能的,能干的
primary : n. 最主要者,原色;a. 主要的,初期的,根本的,原始的,首要的,基本的
responsibility : n. 责任,职责,负担,响应度,可靠性
skill : n. 技术,技巧,技能,熟练,巧妙
fleet : n. 舰队,港湾,小河;a. 快速的,敏捷的,浅的;ad. 浅;vt. 消磨;vi. 疾驰,飞逝,掠过
linger : vi. 逗留,消磨,徘徊;vt. 拖延
usher : n. 带位员,招待员;vt. 引导,展示;vi. 作招待员
severe : a. 严格的,凶猛的,严肃的,严厉的,朴素的,严重的
frost : n. 霜,冰冻,冷漠;vt. 覆着霜,冻结,结霜;vi. 受冻,起霜
drought : n. 干旱,缺乏
hail : n. 冰雹,致敬,招呼;vt. 向...欢呼,致敬,招呼,使象下雹样落下;vi. 招呼,下雹;int. 万岁,欢迎
frustration : n. 打破,挫折,顿挫
await : vt. 等候
wary : a. 小心的,机警的,周到的,唯恐的
maize : n. 玉蜀黍,黄色;a. 玉蜀黍色的,黄色的
adversity : n. 不幸,灾祸,逆境,灾难
feasible : a. 能实行的,可行的,适宜的
stubble : n. 断株,茬,剪成短短的头发
harvest : n. 收获,成果,收获物,收获期;vt. vi. 收割,收获
crop : n. 农作物,产量,平头;vt. 收割,修剪,种植;vi. 收获
vigilance : n. 警戒,警觉心,失眠症
proceed : vi. 进行,开始,发出,继续进行,起诉
shell : n. 贝壳,壳,外形,炮弹;vt. 去壳,脱落,炮轰;vi. 剥落,脱壳;
slate : n. 石板;a. 石板色的;vt. 铺石板,责骂,痛打
immediate : a. 立即的,直接的,近的
consumption : n. 消费,消费量,憔悴
remainder : n. 剩余物,其他的人,残余,余数;vt. vi. 廉价出售;a. 剩余的,出售剩书的
appropriate : a. 适当的
disaster : n. 灾祸,不幸,彻底失败
failure : n. 失败,失败者,不足,缺乏,破产
accompany : vt. 陪伴,带有,为...伴奏;vi. 伴奏,伴唱
staple : n. 主要产物,常用品,主要要素,原料,钩环,订书钉;a. 主要的,重要的;vt. 分类,选择,钉住
squash : n. 压碎的东西,南瓜,拥挤嘈杂的人群;vt. 压扁,镇压,压制;vi. 被压扁,发溅泼声,挤入
slice : n. 薄的切片,一部分,菜刀;vt. 切成薄片,切下;vi. 切
strung : vbl. string的过去式和过去分词string : n. 线,细绳,一串,字串;vt. 串起,成串,收紧,缚,扎;vi. 成一串

The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe is somewhat more than 25 percent helium by weight and somewhat less than 75 percent hydrogen.

Astronomers have measured the abundance of helium throughout our galaxy and in other galaxies as well. Helium has been found in old stars, in relatively young ones, in interstellar gas, and in the distant objects known as quasars. Helium nuclei have also been found to be constituents of cosmic rays that fall on the earth (cosmic "rays"are not really a form of radiation; they consist of rapidly moving particles of numerous different kinds). It doesn't seem to make very much difference where the helium is found. Its relative abundance never seems to vary much. In some places, there may be slightly more of it: in others, slightly less, but the ratio of helium to hydrogen nuclei always remains about the same.

Helium is created in stars. In fact, nuclear reactions that convert hydrogen to helium are responsible for most of the energy that stars produce. However, the amount of helium that could have been produced in this manner can be calculated, and it turns out to be no more than a few percent. The universe has not existed long enough for this figure to be significantly greater. Consequently, if the universe is somewhat more than 25 percent helium now, then it must have been about 25 percent helium at a time near the beginning.

However, when the universe was less than one minute old, no helium could have existed. Calculations indicate that before this time temperatures were too high and particles of matter were moving around much too rapidly. It was only after the one- minute point that helium could exist. By this time, the universe had cooled sufficiently that neutrons and protons could stick together. But the nuclear reactions that led to the formation of helium went on for only a relatively short time. By the time the universe was a few minutes old, helium production had effectively ceased.

重点单词：
elements : n. 原理,基础
helium : n. 氦
quantity : n. 量,数量,总数
accurate : a. 正确的,精确的
abundance : n. 丰富,充足,大量
galaxy : n. 银河,星系,一群显赫的人物
relatively : ad. 相对地
interstellar : a. 星际的
quasar : n. 恒星状球体,半星球体,类星球体
nuclei : n. nucleus 的复数形nucleus : n. 核心,核子,原子核,中坚
constituent : n. 成分,选民,构成物;a. 构成的,组织的,有选举权的
radiation : n. 放射线
consist : vi. 组成,存在,一致
particle : n. 粒子,点,极小量
ratio : n. 比,比率
convert : n. 皈依者,改变宗教者;vt. 使改变信仰,转换,兑换,倒置;vi. 皈依
responsible : a. 有责任的,负责的,责任重大的,可靠的
manner : n. 样子,礼貌,风格
significant : a. 重要的,有效的,有含义的,暗示的,非偶然的
consequently : ad. 结果
indicate : vt. 指出,显示,象征,指示
particle : n. 粒子,点,极小量
sufficient : a. 充分的,足够的
neutron : n. 中子
proton : n. 质子
stick : n. 棍,棒,刺,茎,枯枝,条状物;vt. 插于,刺入,钉住,使停止,伸出,粘贴;vi. 粘住,停留,坚持,陷住,伸出
effectively : ad. 有效地,有力地,实际上
cease : n. 停止;vi. vt. 停止,终了

In colonial America, people generally covered their beds with decorative quilts resembling those of the lands from which the quilters had come. Wealthy and socially prominent settlers made quilts of the English type, cut from large lengths of cloth of the same color and texture rather than stitched together form smaller pieces. They made these until the advent of the Revolutionary War in 1775, when everything English came to be frowned upon.

Among the whole-cloth quilts made by these wealthy settlers during the early period are those now called linsey-woolseys. This term was usually applied to a fabric of wool and linen used in heavy clothing and quilted petticoats worn in the wintertime.Despite the name, linsey-woolsey bedcovers did not often contain linen. Rather, they were made of a top layer of woolen or glazed worsted wool fabric, consisting of smooth, compact yarn from long wool fibers, dyed dark blue, green, or brown with a bottom layer of a coarser woolen material, either natural or a shade of yellow. The filling was a soft layer of wool which had been cleaned and separated and the three layers were held together with decorative stitching done with homespun linen thread. Later, cotton thread was used for this purpose. The design of the stitching was often a simple one composed of interlocking or crossed diagonal lines giving a diamond pattern.

This type of heavy, warm, quilted bedcover was so large that it hung to the floor. The corners are cut out at the foot of the cover so that the quilt fit snugly around the tall tour-poster beds of the 1700's which differed from those of today in that they were shorter and wider; they were short because people slept in a semi-sitting position with many bolsters or pillows, and wide because each bed often slept three or more. The linsey- woolsey covering was found in the colder regions of the country because of the warmth it afforded. There was no central heating and most bedrooms did not have fireplaces.

重点单词：
colonial : a. 殖民的,殖民地的
decorative : a. 装饰的
quilt : n. 棉被;vt. 制成棉被,摘录;vi. 缝被子
resemble : vt. 相似,类似,象
wealthy : a. 富有的,丰裕的,充分的
prominent : a. 卓越的,显著的,突出的,突起的,凸出的
texture : n. 织法,组织
stitch : n. 一针,疼痛,针法,碎布条,针脚;vt. vi. 缝,缝合,装订
advent : n. 来到,来临,耶稣降临时
frown : n. 皱眉;vi. 皱眉头;vt. 皱眉表示 frown upon 不赞成 不同意
fabric : n. 织物,布,建筑物,结构,构造
linen : n. 亚麻布,亚麻线,亚麻制品;a. 亚麻布制的,亚麻的
petticoat : n. 衬裙,裙子
bedcover : n. 被面
glaze : n. 釉,上光,光滑面;vt. 装以玻璃,上釉于;vi. 变成为光滑,变呆滞
smooth : a. 平滑的,平坦的,平稳的,调匀的,和蔼的,无毛的,流畅的,圆滑的,安祥的;vt. 使光滑,烫平,使优雅,消除;vi. 变平滑,变平静;n. 一块平地,平滑部分
compact : a. 紧凑的,紧密的,简洁的;vt. 使装满,使简洁;vi. 变紧密
yarn : n. 纱,纱线,故事
fiber : n. =fibre;光纤
coarse : a. 粗糙的,下等的,粗俗的;a. 粗略的
shade : n. 荫,阴暗,荫凉处,底纹,浓淡,遮光物,帘,灯罩,些微;vi. 渐变;vt. 使阴暗,使渐变,遮蔽,微减
filling : n. 充填物,填料,填土
spun : vbl. spin的过去式和过去分词;a. 纺成的
thread : n. 线,丝,纤维,线索;vt. 穿线于,穿过,通过,使交织;vi. 通过
interlocking : a. 联锁的
diagonal : a. 对角线的,斜的,斜纹的;n. 对角线,斜线,斜列
corner : n. 角落,转角,窘境;vt. 迫至一隅,垄断,使陷入绝境;vi. 相交成角,囤积
snugly : ad. 舒适地,整洁干净地,情况极好地
semi : pref. 半
bolster : n. 支持,长枕;vt. 支持,支撑
pillow : n. 枕头;vt. 作...的枕头,垫,枕于;vi. 靠在枕上
warmth : n. 温暖,温情,暖和,激动,生气
afford : vt. 提供,供应得起,给予

Growing tightly packed together and collectively weaving a dense canopy of branches, a stand of red alder trees can totally dominate a site to the exclusion of almost everything else, certain species such as salmonberry and sword ferns have adapted to the limited sunlight dappling through the canopy, but few evergreen trees will survive there; still fewer can compete with early prodigious growth of alders. A Douglas fir tree reaches its maximum rate of growth ten years later than an alder, and if the two of them begin life at same time, the alder quickly outgrows and dominates the Douglas fir, after an alder canopy has closed , the Douglas fir suffers a marked decrease in growth, often dying within seven years. Even more shade-tolerant species of trees such as hemlock may remain badly suppressed beneath aggressive young alders.

Companies engaged in intensive timber cropping naturally take a dim view of alders suppressing more valuable evergreen trees. But times are changing; a new generation of foresters seems better prepared to include in their management plans consideration of the vital ecological role alders play.

Among the alder's valuable ecological contributions is its capacity to fix nitrogen in nitrogen-deficient soils. Alder roots contain clusters of nitrogen-fixing nodules like those found on legumes such as beans. In addition, newly developing soils exposed by recent glacier retreat and planted with alders show that these trees are applying the equivalent of ten bags of high-nitrogen fertilizer to each hectare per year. Other chemical change to soil in which they are growing include a lowering of the base content and rise in soil acidity, as well as a substantial addition of carbon and calcium to the soil.

Another important role many alders play in the wild, particularly in mountainous areas, is to check the rush of water during spring melt. In Japan and elsewhere, the trees are planted to stabilize soil on steep mountain slopes. Similarly, alders have been planted to stabilize and rehabilitate waste material left over from old mines, flood deposits, and landslide areas in both Europe and Asia.

重点单词：
tightly : ad. 紧紧地,坚固地
pack : n. 包裹,一群,一副,背包,包装;vt. 包装,捆扎,塞满,压紧,挑选;vi. 包装货物,挤,群集,被包装;背包
collective : a. 集体的,聚集的,共同的
weave : n. 编法,织法,编织;vt. 编织,组合,编排,使迂回前进;vi. 纺织,迂回行进,摇晃
dense : a. 密集的,浓厚的
canopy : n. 天篷,遮篷,苍穹;vt. 用天蓬遮盖
alder : n. 桤木
dominate : vt. vi. 支配,占优势
exclusion : n. 排除,除外,逐出
sword : n. 刀,剑,战争,武力
fern : n. 蕨类植物
adapt : vt. 使适应,改编;vi. 适应
dapple : n. 斑纹,花马;a. 有斑纹的;vt. vi. (使)起斑纹
survive : vt. 生存,生还,幸免于;vi. 活下来,幸存
prodigious : a. 很大的,惊人的,异常的
fir : n. 枞树,杉木
maximum : n. 极点,最大量,极大;a. 最高的,最大的,最大极限的
outgrow : vt. 过大而不适于,出生,长出
suffer : vt. 遭受,经验,忍受;vi. 受痛苦,受损害
decrease : n. 减少,减少之量;vi. vt. 减少
tolerant : a. 宽容的,宽大的,默认的
hemlock : n. 毒胡萝卜,铁杉
suppress : vt. 镇压,使止住,禁止,抑制,查禁
aggressive : a. 侵略的,攻击性的,进取的
engage : vi. 答应,从事,交战;vt. 使忙碌,雇佣,预定,使从事于,使参加
intensive : a. 加强的,集中的;n. 加强器
timber : n. 木材,木料;vt. 用木材建造
croppy : n. 剪短发的人
dim : a. 暗淡的,模糊的;vt. 使暗淡
generation : n. 一代,一世,产生
forester : 林业居民；护林人员；林业动物
consideration : n. 考虑,原因
vital : a. 重要的,生命的,充满活力的,生死攸关的,致命的
ecological : a. 生态学的,社会生态学的
contribution : n. 捐助,捐助之物,贡献
capacity : n. 容量,能力,才能,资格;n. 容量
nitrogen : n. 氮
deficient : a. 不足的,不充分的,有缺陷的
cluster : n. 串,丛,群,簇;vi. 成串,丛生;vt. 使聚集
nodule : n. 小节,小瘤,小结节
legume : n. 豆类,豆荚
exposed : a. 暴露的,无掩蔽的,暴露于风雨中的
retreat : n. 休息寓所,撤退,隐居,退避,避难所;vi. 撤退,隐退,放弃,向后倾;vt. 退(棋)
equivalent : n. 同等物,等价物,相等物;a. 相等的,相当的,同意义的
fertilizer : n. 肥料,受精媒介物
hectare : n. 公顷
lowering : a. 使卑劣的,减弱体力的,昏暗的
substantial : n. 重要部分,本质;a. 实质上的,物质的,有内容的,结实的
carbon : n. 碳,副本,复写纸
calcium : n. 钙
melt : n. 熔化,熔化物,溶解;vt. vi. (使)熔化,(使)溶解,(使)消散,(使)变软
stabilize : vt. 使安定,使坚固;vi. 稳定,安定
steep : n. 浸渍,浸液,悬崖;a. 险峻的,陡峭的,急剧升降的,不合理的,夸大的;vt. vi. 浸,泡
slope : n. 倾斜,斜坡,斜率,掮枪的姿势;vt. 使倾斜,弄斜,掮;vi. 倾斜,逃走
rehabilitate : vt. 恢复原状,修复,使恢复
flood : n. 洪水,大量之水,涨潮;vt. 使泛滥,注满,淹没;vi. 被淹,溢出,涌进
deposit : n. 存款,定金,堆积物;vt. 存放,堆积;vi. 沉淀
landslide : n. 山崩

In taking up a new life across the Atlantic, the early European settlers of the United States did not abandon the diversions with which their ancestors had traditionally relieved the tedium of life. Neither the harshness of existence on the new continent nor the scattered population nor the disapproval of the clergy discouraged the majority from the pursuit of pleasure.

City and country dwellers, of course, conducted this pursuit in different ways. Farm dwellers in their isolation not only found it harder to locate companions in play but also, thanks to the unending demands and pressures of their work, felt it necessary to combine fun with purpose. No other set of colonists took so seriously on expression of the period, "Leisure is time for doing something useful." In the countryside farmers therefore relieved the burden of the daily routine with such double-purpose relaxations as hunting, fishing, and trapping. When a neighbor need help, families rallied from miles around to assist in building a house or barn, husking corn, shearing sheep, or chopping wood. Food, drink, and celebration after the group work provided relaxation and soothed weary muscles.

The most eagerly anticipated social events were the rural fair. Hundreds of men, women, and children attended from far and near. The men bought or traded farm animals and acquired needed merchandise while the women displayed food prepared in their kitchens, and everyone, including the youngsters, watched or participated in a variety of competitive sports, with prizes awarded to the winners. These events typically included horse races, wrestling ,matches, and foot races, as well as some nonathletic events such as whistling competitions, No other occasions did so much to relieve the isolation of farm existence.

With the open countryside everywhere at hand, city dwellers naturally shared in some of the rural diversions. Favored recreations included fishing, hunting, skating, and swimming. But city dwellers also developed other pleasures, which only compact communities made possible.

重点单词：
across : ad. 横过,交叉,到另一边,在对面,成十字;prep. 横过,穿过,交叉,在...的对面
Atlantic : n. 大西洋;a. 大西洋的
abandon : vt. 放弃,抛弃,遗弃,使屈从,放纵 n. 放任,狂热,沉溺,无拘束
diversion : n. 转移
relieve : vt. 减轻,救济,解除,使免除,调剂,使显著,换...的班,衬托,使不单调;vi. 救济,换防,成浮雕
tedium : n. 厌烦,沉闷
harshness : n. 粗糙的事物,刺耳,严肃
scatter : n. 消散,分散,散播,散布,酒馆,散射;vi. 散布,散播,消散;vt. 使消散,使分散,撒,散射,散播,散布
disapproval : n. 不赞成
clergy : n. 圣职者,牧师,僧侣,神职人员
majority : n. 多数,大半
pursuit : n. 追踪,追捕,追求,追赶,工作,职业
dweller : n. 居民
conduct : n. 行为,举动,指导;vt. 引导,指挥,管理,实施;vi. 引导,传导,指挥
isolation : n. 隔绝,孤立,隔离
unending : a. 无穷尽的,无止境的,不停的
felt : n. 毛毯,毡;vt. 制毡,使粘结;vi. 粘结;vbl. feel的过去式和过去分词
necessary : n. 必需品,日用品;a. 必需的,必要的,必然的
expression : n. 表达,语法,措辞
leisure : n. 空闲,闲暇,悠闲;a. 空闲的,有闲的
burden : n. 负担,重载,担子,责任;vt. 装货于,麻烦,使负担
trapping : n. 设陷,陷入,俘获
rally : n. 重振旗鼓,集合,示威运动,价格回稳;vt. vi. 重整旗鼓,集合,恢复精神,挖苦,团结,嘲笑
assist : n. 帮助,协助;vt. 帮助,搀扶;vi. 协助,参加
barn : n. 谷仓
husk : n. 外壳,皮,无价值之物;vt. 剥...的壳,削皮
shearing : n. 剪羊毛,剪取的羊毛
chop : n. 厚肉片,排骨,砍,戳记,商标,交换;vt. 剁碎,砍,切,割断;vi. 砍,突然转向
soothe : vt. 缓和,使安静,安慰,奉承;vi. 起安慰作用
weary : a. 疲倦的,萎靡的,厌倦的,厌烦的;vt. 使疲倦,使厌烦;vi. 疲乏,生厌,不耐烦
eager : a. 热心的,渴望的,热望的
anticipate : vt. 预期,占先,提前使用
fair : n. 展览会,市集,美好的事物;a. 公平的,晴朗的,美丽的;ad. 公平地,清楚地;vi. 转晴
acquired : a. 已取得的,已获得的,已成习惯的,后天的
merchandise : n. 商品,存货;vi. vt. 交易,买卖
display : n. 显示,陈列,炫耀,显示器;vt. 显示,表现,夸示
youngster : n. 年青人,少年
participate : vi. 参加,分享,参与;vt. 分享,分担
competitive : a. 竞争的
award : n. 奖品,决定,判决;vt. 颁发,赏给
wrestling : n. 摔角,扭斗,格斗
athletic : a. 运动的
whistle : n. 口哨,汽笛,啸啸声,口哨声;vi. 吹口哨,鸣汽笛,发嘘嘘声;vt. 用口哨通知,用口哨演奏
occasion : n. 场合,时机,机会,诱因,理由;vt. 致使,惹起,引起
share : n. 部分,参与,一份,共享,份额,参股;vt. 均分,分担,分享,分配,共有;vi. 分享;n. DOS命令:使之支持文件的共享和锁定
diversion : n. 转移
skating : n. 溜冰
possible : a. 可能的,潜在的,合理的;n. 可能性,可能的事物